Over the last decade or so, large electronic systems such as telephone switching facilities or main frame computers and the like, have demonstrated a convergence of technologies. Likewise these apparatus have been taking on a general sameness of appearance, particularly in the retainment of circuit board elements. Each of the systems of interest is characterized by an equipment shelf having card sliders being arranged in parallel one with another, in a row, for receiving edge surfaces of a plurality of circuit boards. A circuit board is typically of about one square foot in area and is electrically or optically connected into the system by interconnecting conductors carried by a back plane at one side of the equipment shelf. Equipment shelves, which at a glance may appear to be similar, have remained distinct because of design variations in circuit board widths which of course dictate like differences in the lateral spacing of the circuit board sliders. Distinct variations in system capacities and features often dictate similar variations in the physical arrangement of circuit boards of various widths in each equipment shelf.
It has been common practice to manufacture a basic design of equipment shelf with variable or adaptable spacing being provided by a multitude of closely spaced mounting orifices, so that virtually any combinations of lateral spacing requirements could be provided for by selective placement of plastic card sliders However, it has been realized that this arrangement is prone to permitting misplaced installation of card sliders, and in some production line environments, it has been found to encourage thoughtless insertion of card sliders at every possible location. Such practice necessitates subsequent correction before circuit boards or units can be inserted into the system. Of course correction includes the removal of any misplaced card sliders from those locations where they had been fastened. Such insertion and subsequent removal is accompanied by abrasion or wearing of the plastic card slider such that if the card slider were to be reused at some other location, the degree of interference with the mounting orifices is reduced. Hence reliability of fastening cannot be relied upon and immediate disposal of any removed card sliders is preferable to avoid any confusion between new and used card sliders at the manufacturing facility.
An alternate practice has been that of providing only the mounting orifices peculiar to the particular equipment shelf. The mounting orifices are formed within cross connecting members in the structure. The typical equipment shelf is usually constructed from several piece parts which are peculiar to the equipment shelf. It is the dimensions and assemble of the piece parts which define the particular characteristics of the shelf. As such, a manufacturer which is in the process of manufacturing several such electronic systems, at the same time, must require an extensive inventory of piece parts for manufacturing all of the different equipment shelves. Many of the piece parts are the cross connecting members which differ only in the location and number of the mounting orifices but nonetheless contribute to the stocking of a large and expensive inventory. Some manufacturers have found that fool proof avoidance of misplaced and or unreliably secured card sliders is worth the additional expense.
It is an object of the invention to reduce the expense of inventory associated with the variety and number of piece parts typically required for the manufacture of various equipment shelves used in some electronic systems.